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close this bookPublic Health Response to Biological and Chemical Weapons - WHO Guidance (WHO; 2004; 357 pages) [ES] [RU] View the PDF document
View the documentForeword
View the documentAcknowledgements
View the documentExecutive summary
View the documentAbbreviations and acronyms
View the documentContributors
open this folder and view contents1. INTRODUCTION
open this folder and view contents2. ASSESSING THE THREAT TO PUBLIC HEALTH
open this folder and view contents3. BIOLOGICAL AND CHEMICAL AGENTS
View the document4.1 Background
open this folder and view contents4.2 Preparedness
open this folder and view contents4.3 Response
open this folder and view contents5. LEGAL ASPECTS
open this folder and view contents6. INTERNATIONAL SOURCES OF ASSISTANCE
View the documentANNEX 1: Chemical agents
View the documentANNEX 2: Toxins
View the documentANNEX 3: Biological agents
View the documentANNEX 4: Principles of protection
View the documentANNEX 5: Precautions against the sabotage of drinking-water, food, and other products
View the documentANNEX 6: Information resources
View the documentANNEX 7: Affiliation of who member states to the international treaties on biological and chemical weapons


On 20 March 1995, a terrorist group launched a coordinated attack with the nerve gas sarin on commuters on the Tokyo subway system. This highly publicized attack killed 12 people and caused more than 5000 to seek care. Without the prompt and massive emergency response by the Japanese authorities, and some fortunate mistakes by the terrorist group, the incident could have been much more devastating. While this is the most widely publicized incident of this type, it is not the first nerve-gas attack in Japan. In June 1994, 7 people were killed and more than 300 injured in an attack by the same group on a residential apartment building in Matsumoto. In December 1994, an opponent of the group was murdered by the skin application of VX.

This Appendix provides a brief summary of the background and features of these incidents and the lessons learned from them. It draws heavily on a number of excellent and comprehensive reviews that have appeared in the international literature (1 - 6).


The Aum Shinrikyo sect was the brainchild of Chizuo Matsumoto, whose childhood aspirations apparently included the leadership of Japan. In 1984, he started a small publishing house and yoga school, which gradually developed into a cult. He renamed himself Shoko Asahara ("Bright Light"), embarked on a course of cult expansion, with increasingly bizarre teachings and rituals for devotees, and ultimately subversion with the aim of achieving supremacy for his followers in Japan. The group attracted a surprisingly large international membership, numbering in the tens of thousands, and actively recruited graduate scientists and technicians to develop armament programmes that were highly ambitious in their scope. Plans included the development and use of biological and chemical weapons.

Aum Shinrikyo’s chemical weapons made worldwide news after the Tokyo subway attack in 1995, but a quest for biological weapons actually pre-dated the chemical programme. Despite the expenditure of large sums of money and great efforts to acquire the means to develop and disseminate biological agents, attempted attacks (with botulinum toxin in April 1990 and anthrax in 1993) failed, fortunately causing no noticeable effects on the target population of Tokyo.

The cult had more success with its chemical programme, which was launched in 1993 and reportedly cost around US$ 30 million. After experiments with VX, tabun, soman, mustard gas, hydrogen cyanide and phosgene, the cult’s final choice was the nerve gas sarin, and a plan was developed for the production of about 70 tonnes of this substance at Aum Shinrikyo’s facilities in Kamikuisiki, at the foot of Mount Fuji.

The Matsumoto incident

During 1994, Aum Shinrikyo was involved in legal proceedings concerning a land purchase, and a gas attack on the overnight premises of the three judges involved was planned for 27 June of that year, apparently to pre-empt an unfavourable ruling. An improvised sarin-dissemination system was used, consisting of a heater, fan and drip system, sarin vapour being vented from the window of a disguised delivery van. After a 20-minute release period, the gas spread over an elliptical area measuring about 800 by 570 metres (most effects occurring within a smaller area of 400 by 300 metres). While the judges survived, 7 unfortunate residents died as a result of the attack, there were 54 other hospital admissions, and 253 persons sought care at outpatient facilities. In the absence of formal identification of the toxic substance, doctors could rely only on what they observed to guide treatment, namely clinical symptomatology consistent with organophosphate poisoning. On 4 July, an official report revealed that the cause of the poisoning had been the chemical warfare agent sarin, which had been identified by gas chromatography - mass spectrometry (GC - MS) in a water specimen taken from a pond in the affected area. No evidence found at that time incriminated Aum Shinrikyo.

The Tokyo incident

The Japanese authorities were collecting increasing evidence suggestive of Aum Shinrikyo’s interest in chemical weapons. Ironically, they had been unable to prevent the suspected acquisition or production of chemical weapons’ since such activities were not illegal at that time. The pretext for a raid on the suspected production plant was provided when evidence linked an Aum member to a suspected kidnapping, but cult members employed by the authorities warned Asahara of the imminent raid, for which the police were being trained in chemical defence. In an apparent attempt to dissuade the police from making the raid, an attack on the Tokyo subway system was hastily planned. On the morning of 20 March 1995, five two-man teams carried out the attack, each team consisting of one getaway driver and one subway rider. Four subway riders carried two double-layered plastic bags and one rider carried three, each bag containing about half a litre of sarin. The sarin was only about 30% pure because it had been hastily produced for use in the attack. Five subway lines converging on the station of Kasumigaseki (where many Japanese government buildings and the Tokyo Metropolitan Police Department are located) had been selected. At around 08:00, i.e. during peak commuting time, the five assailants placed their sarin-filled bags on the train floor, pierced them with sharpened umbrella tips,7 and left the trains several stations away from Kasumigaseki.

7 Of the 11 bags, only 8 were actually ruptured: 3 were subsequently recovered intact. It is estimated that around 4.5 kg of sarin were released.

The first emergency call was received by the Tokyo fire department at 08:09, and the emergency services were soon inundated with calls for aid from the numerous subway stations where affected passengers were disembarking and seeking medical help. A total of 131 ambulances and 1364 emergency medical technicians were dispatched, and 688 people were transported to hospital by the emergency medical and fire services. More than 4000 people found their own way to hospitals and doctors using taxis and private cars or on foot. The lack of emergency decontamination facilities and protective equipment resulted in the secondary exposure of medical staff (135 ambulance staff and 110 staff in the main receiving hospital reported symptoms).

Having initially been misinformed that a gas explosion had caused burns and carbon monoxide poisoning, medical centres began treating for organophosphate exposure based on the typical symptomatology encountered, supported by the results of tests indicating depressed acetylcholinesterase activity in symptomatic victims (see Annex 1). An official announcement by the police that sarin had been identified reached the hospitals, via the television news, about three hours after the release.

Overall, 12 heavily exposed commuters died, and around 980 were mildly to moderately affected, while about 500 required hospital admission. More than 5000 people sought medical assistance.


Much can be learned from the analysis of these attacks, at both the general level (i.e. in terms of the international threat), and at the specific level (i.e. in terms of the immediate effect and response).

• Magnitude of the event. While the human consequences of the attack should not be underestimated, they should also not be exaggerated. The frequently encountered casualty toll of "over 5000" must be seen in its true perspective. The attack was serious - 12 people died, 54 were severely injured, and around 980 were mildly to moderately affected. The majority of the 5000 seeking help, many of them with psychogenic symptoms, were (understandably) worried that they might have been exposed. This demonstrates the value of rapid information dissemination via the media in reassuring the public. It also shows the importance of effective triage at receiving centres in ensuring that medical resources are reserved for those who really have been exposed. Before this attack is taken as evidence of the effectiveness of toxic chemicals in the hands of terrorists, however, the figure of 12 dead should be compared with the death tolls of recent terrorist attacks using conventional explosives, such as the bombing of the United States embassies in Nairobi and Dar es Salaam (257), the Federal Building in Oklahoma City, USA (168), and the United States Marine barracks in Lebanon (241). These, in turn, must now be regarded as relatively slight in comparison with what happened on 11 September 2001, when hijacked long-haul passenger aircraft were flown into the Pentagon outside Washington, DC, and into each of the twin towers of the World Trade Center in New York City, killing, it is now believed, more than 3100 people. Equally, it should be realized that the sarin casualty figures might have been many times worse.

• The utility of chemical weapons in achieving terrorist objectives. While many reports (particularly in the media) have touted the sarin incidents as evidence of a frightening new era in terrorist methodology, a sober assessment of the actual results shows otherwise. It is true that, before 11 September 2001, this was one of the most highly publicized terrorist attacks in history. The result for Aum Shinrikyo, however, can hardly be judged a success. The immediate objective of the attack was the disruption of an anticipated raid on cult premises and, on a broader level, the incitement of social upheaval. In fact, the raid was delayed for only 48 hours, the Japanese Government remained firmly in power, and most of the cult’s senior members are now in prison.

• The ease of acquisition and use of biological and chemical weapons. Despite its ample financial resources, equipment and expertise, and years in which to develop its weapons, Aum Shinrikyo attempted but failed to use biological agents effectively (7 - 9) and achieved only relatively limited success with its chemical programme. Aspirant terrorists thinking of using biological or chemical weapons may well find these results a deterrent, not an encouragement.

• The importance of national legislation on chemical weapons. Despite compelling evidence of the cult’s growing interest in chemical agents, which started well before the Tokyo subway attack, no Japanese laws prohibited its activities at the time, and pre-emptive action could therefore not be taken. Since the entry into force of the CWC in 1997, however, all Member States (including Japan) have been able to share their experiences and planning concepts to fulfil their obligation to enact and implement legislation forbidding persons on their territory, or under their jurisdiction, from undertaking any activities that are prohibited to the State Party itself.8 When such legislation has been introduced, pre-emptive action against terrorist groups developing or using chemical weapons can be taken. Likewise, the entry into force of the BWC in 1975 has obliged all its States Parties (including Japan) to take the measures necessary for its implementation

• The importance of detection and identification abilities. In both the Matsumoto and Tokyo incidents, medical staff had to rely on clinical observation to guide their initial treatment of victims. If portable detection apparatus had been available to emergency-response personnel, this would have facilitated the earlier identification of the nature of the event. The follow-up forensic and legal process was considerably aided by the laboratory identification of sarin using sophisticated GC - MS techniques available to the police forensic toxicologists (10). In an interesting development of new biomedical testing methods, scientists in the Netherlands were later able to retrieve sarin from the stored blood samples of 10 out of 11 of the victims of the Tokyo incident, and from 2 out of 7 samples from the Matsumoto incident - unequivocal evidence of exposure to sarin (11).

• The importance of decontamination abilities and protection. About 10% of the ambulance staff who responded to the incident reported symptoms of exposure, as did 110 members of the staff at the major receiving hospital (although these symptoms were generally mild). A contributing factor was the lack of decontamination facilities on site and of protective equipment for initial responders and hospital staff. Before this is taken to mean that high-level protection is always required, it should be remembered that the figure of 10% reporting mild effects also means that at least 90% were not affected at all. A reasonable conclusion is that the availability of protective equipment would have been of considerable benefit to responders. However, an approach based on graded protection appropriate to the level of contamination is required to prevent the unnecessary immobilization of helpers as a result of the ergonomic problems of wearing protective clothing (see Annex 4). Rapidly deployable decontamination equipment is needed both on site (to avoid secondary contamination of emergency transport) and at receiving facilities. However, it is important to remember that the majority of people who sought medical help did so on their own initiative and using their own transport. This would have effectively negated much of the utility of on-site decontamination systems, even had they been available, as they would generally be used for victims being treated in the course of evacuation by the emergency services.

• The importance of command, control and communication. Communication channels available to emergency-response personnel were not able to cope with the flood of calls that the attack precipitated. In particular, overload prevented effective communications between the on-site and mobile emergency medical technicians and their supervising hospital-based doctors, whether to seek medical instructions or to determine which hospitals could receive patients. As a result, a number of patients did not benefit from interventions such as airway support, intubation or intravenous therapy until after they arrived at hospitals. The timely provision of accurate information to responders is crucial to their own safety and to their ability to provide appropriate assistance. Preplanned systems for tapping the expert knowledge of experienced toxicologists, poison information centres and chemical warfare specialists would have been of major assistance to the receiving medical facilities. A single responsible local authority with the ability to communicate with, and coordinate the activities of, the various response elements would have been a considerable advantage. Complicated formalities and the need for high-level approval prevented the rapid mobilization of the specialists in chemical defence within the Japanese military.

• The readiness of medical personnel to handle chemical casualties. The majority of the Tokyo hospital staff, like medical personnel in most parts of the world, were untrained in the care of casualties caused by chemical weapons and had no immediate access to treatment protocols for the victims of such weapons. This is not something that can be left to military specialists, as it is the local hospitals that will be the first to receive the casualties. Inclusion of the effects of chemical weapons and treatment of the resulting casualties both in standard medical curricula and in the training of first responders and the staff of local hospital accident and emergency departments, is an essential component of medical preparedness for responding to chemical incidents.

8 See also Appendix 5.2.


The release of sarin by a terrorist group in Japan resulted in a highly publicized incident with mass casualties. In scale, however, it did not approach the human and environmental toll that has resulted from a number of recent terrorist attacks using conventional explosives, and it falls far short of what happened in the United States on 11 September 2001. Despite many difficulties, Japanese emergency units and local hospitals were able to achieve a remarkably rapid response, without which the casualty figures might have been considerably higher. While analysis of the event reveals a number of important lessons for authorities to consider when preparing for such incidents, it also reveals many of the technical difficulties associated with toxic chemicals and their limitations as weapons for use by terrorist groups.


1. Smithson AE. Rethinking the lessons of Tokyo. In: Smithson AE, Levy LA, eds. Ataxia: the chemical and biological terrorism threat and the US response. Washington, DC, The Henry L. Stimson Center, 2000, 71 - 111 (Report No. 35).

2. Tu AT. Overview of sarin terrorist attacks in Japan. In: Natural and selected synthetic toxins: biological implications. Washington, DC, American Chemical Society, 2000:304 - 317 (American Society Symposium Series, No. 745).

3. Okumura T et al. Tokyo subway Sarin attack: disaster management. Part 1: community emergency response. Academic Emergency Medicine, 1998, 5:613 - 617.

4. Okumura T et al. Tokyo subway Sarin attack: disaster management. Part 2: hospital response. Academic Emergency Medicine, 1998, 5:618 - 624.

5. Okumura T et al. Tokyo subway Sarin attack: disaster management. Part 3: national and international responses. Academic Emergency Medicine, 1998, 5:625 - 628.

6. Kulling P. The terrorist attack with sarin in Tokyo. Socialstyrelsen report. Stockholm, Modin-Tryck, 2000.

7. Leitenberg M. Aum Shinrikyo’s efforts to produce biological weapons. Terrorism and Political Violence, 1999, 11(4):149 - 158.

8. Smithson A, Levy LA. Ataxia: the chemical and biological terrorism threat and the US response. Washington, DC, The Henry L. Stimson Center, 1999.

9. Takahashi H et al. The Kameido incident: documentation of a failed bioterrorist attack. Poster presented at the 4th International Conference on Anthrax, St John’s College, Annapolis, MD, USA, 10 - 13 June 2001.

10. Seto Y et al. Toxicological analysis of victims’ blood and crime scene evidence samples in the Sarin gas attack caused by the Aum Shinrikyo cult. In: Natural and selected synthetic toxins: biological implications. Washington, DC, American Chemical Society, 2000, 318 - 332 (American Chemical Society Symposium Series, No. 745).

11. Polhuijs M, Langenberg JP, Benschop HP. New method for retrospective detection of exposure to organophosphorus anticholinesterases: application to alleged Sarin victims of Japanese terrorists. Toxicology and Applied Pharmacology, 1997, 146:156 - 161.

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